The present invention relates to a foot orthosis and, more particularly, to an orthopedic appliance for correctably realigning and repositioning specific anatomic segments of the human foot.
In describing the motions which can occur within the subtalar and midtarsal joints, it is important to realize that the axis of motion of these two important joints is not perpendicular to any one body plane. Therefore, the resultant motion which occurs is considered a tri-planar or complex motion. The complex motions which occur at the subtalar and midtarsal joints are called pronation and supination.
Subtalar joint pronation is a complex triplanar motion which essentially will "unlock" the bones of the foot and render the foot loose and mobile. This feature is particularly useful at heel strike so that the foot can effectively adapt to the supporting surface. As the foot pronates, the calcaneus or heel bone everts and the talus above adducts and plantarflexes. This is also accompanied by an internal rotation of the lower extremity. Pronation of the subtalar joint is a necessity since by permitting this motion between these two bones, thus facilitating flexion of the knee above, it becomes a very effective attenuator of the impact shock which can be as high as 2.5 times body weight.
Supination, on the other hand, is the opposite of pronation. It is essentially a motion that "locks" the various bones of the foot together in order to convert our "loose mobile bag of bones", so to speak, into a more rigid lever in preparation for the transfer of body weight distally toward the toes. The motion consists of an inversion of the calcaneus and abduction and dorsiflexion of the talus and an external rotation of the lower extremity, thus facilitating extension of the knee.
Pronation in and of itself is a very healthy and necessary motion to permit a gait which is both efficient and low in impact shock. It is when this pronatory motion is abnormally prolonged or excessive that problems develop both within the foot and more proximally in other body joints, i.e., ankle, knee, and hip.
By comparison, the midtarsal joint, which determines and/or permits movement of the forefoot on the rearfoot, functions around two axes of motion; a longitudinal axis and an oblique axis. The longitudinal axis permits primarily inversion and eversion of the forefoot; while the oblique axis allows primarily abduction and dorsiflexion of the forefoot or a combination of adduction and plantarflexion of the forefoot on the rearfoot. The two axes function not only concurrently to permit a pronatory/supinatory motion of the forefoot to take place but also separately to permit clinically observable independent oblique or longitudinal axis motion to take place.
If the forces which are entering the feet are abnormal, excessive, misdirected or mal-phasic, the ability of the foot to perform its function segmentally and sequentially will be disturbed. Previous therapeutic or assistive approaches have failed to address the combination of factors affecting foot function. While biomechanical or functional foot orthoses attempted this, their "uni-body" construction actually intensified some of the problems:
1. By causing lifting of the lateral column of the foot in mid-stance phase, thus, making the longitudinal joint-to-ground angle more acute and destabilizing the lateral column.
2. By preventing the medial column from lowering itself sufficiently to achieve its adaptive function or by allowing the medial column to lower too much, thus preventing the phasic restoration of the medial column position.
3. By tilting the forefoot position too much or too little in a varus or valgus position (i.e., fixed inversion or fixed eversion position), thereby allowing forefoot orthotic corrections which should function in midstance and/or propulsive phase to influence and disrupt the function of the rearfoot in the earlier occurring contact phase.
4. By the inability of the orthoses because of the "uni-body" construction to adapt to the changing positions, lengths and widths of the foot occurring because of dynamic function.
5. By preventing the first ray from functioning independently from the lesser metatarsals and/or preventing the lesser metatarsals from functioning independently from the first ray complex.
6. By essentially ignoring the all-important oblique axis of the midtarsal joint, thus disallowing any stabilization of the lateral and, therefore, medial columns of the foot during the propulsive phases of gait. Thus, single, continuous non-segmented, biomechanical foot orthoses which attempt to supply control primarily on the frontal plane are incapable of adjusting to the changing functional positions of the various foot segments as they go through their phasic structural and muscular repositioning in an attempt to achieve their normal stabilization and propulsion. Other foot orthotic devices which attempted stabilization failed to address the aspects of muscular force vectors, angular osseous relationships, the subtalar joint axis, the longitudinal and oblique axes of the midtarsal joint, and the tri-plane motions involved with corresponding phasic muscle activities.
Accordingly, it is an object of the present invention to provide a foot orthosis which is capable of adjusting to the varying positions and activities of the human foot in a manner which maximizes the body's own muscular, neurologic and skeletal functions.
Another object is to provide such a foot orthosis which is able to mobilize, restrict or enhance certain motions by altering the angular relationships of the osseous structures of the feet which, together with phasic muscle activity, are responsible for the unlocking and locking (adaptive and propulsive) mechanisms in the feet.
A further object is to provide such a foot orthosis which permits control of the degree of positional change in a sequential manner.
It is also an object to provide such a foot orthosis comprised of components modularly assemblable to meet the particular needs of a given patient.